Number Of Simultaneous Transmissions Research Articles

Capacity Performance for Full-Duplex Multihop Wireless Networks Using Channel Interference Balancing Allocation Scheme.

Full-duplex (FD) communication has been attractive as one of the research interests related to spectrum utilization for wireless networks from the previous evolution of communication systems. Previous studies discuss the realization of the FD system by focusing on self-interference cancellation and transmit power control in low-power wireless network scenarios. Today, capacity maximization is a key challenge in FD multihop wireless networks, in which the multi-channel allocation may lead to imbalance interference power due to the different number of simultaneous transmissions and its group selection that occurred on the same sub-channels. In this paper, we focus on the capacity maximization of the FD system by considering the influence of total interference power on each sub-channel and how to balance by selecting the different number of simultaneous transmissions to form a group that leads to a minimum difference in the total interference power on those sub-channels. Therefore, a channel interference balancing allocation (CIBA) scheme for balancing the total interference power in the multi-channel multihop wireless networks is proposed and further investigated by the idea of cooperative transmission. We also adopt the concept of interference distance to overcome the interference balancing problem of the proposed CIBA scheme. Performance evaluation results reveal that the proposed CIBA scheme achieves lesser total interference power and higher achievable capacity than other fixed channel allocation schemes.

Transmission and Reception Alignment for User Equipment Energy Efficiency in LTE Networks

Energy efficiency has become an essential component in the design of communication protocols, especially for battery-enabled user equipment (UE) devices such as smartphones. In this letter, an energy-efficient UE packet scheduling scheme for LTE/LTE-Advanced cellular networks is proposed. It achieves energy savings by promoting the simultaneous occurrence of transmissions and receptions. Simulation results show that this approach improves the energy efficiency of the device by increasing the number of simultaneous transmissions and receptions; the network performance, however, suffers little impact.

Multi-Channel Distributed DSA Networks: Connectivity and Rendezvous Tradeoffs

In this paper, we investigate and characterize the effects of multi-channel and rendezvous protocols on the connectivity of dynamic spectrum access networks using percolation theory. In particular, we focus on the scenario where the secondary nodes have plenty of vacant channels to choose from a phenomenon which we define as channel abundance. To cope with the existence of multi-channel, we use two types of rendezvous protocols: naive ones which do not guarantee a common channel and advanced ones which do. We show that, with more channel abundance, even with the use of either type of rendezvous protocols, it becomes difficult for two nodes to agree on a common channel, thereby, potentially remaining invisible to each other. We model this invisibility as a Poisson thinning process and show that invisibility is even more pronounced with channel abundance. Following the disk graph model, we represent the multiple channels as parallel edges in a graph and build a multi-layered graph (MLG) in $\boldsymbol {\mathcal {R}}^{\mathbf{2}}$ . In order to study the connectivity, we show how percolation occurs in the MLG by coupling it with a typical discrete percolation. Using a Boolean model and the MLG, we study both cases of primaries’ absence and presence. For both cases, we define and characterize connectivity of the secondary network in terms of the available number of channels, deployment densities, number of simultaneous transmissions per node, and communication range. When primary users are absent, we derive the critical number of channels which maintains super-criticality of the secondary network. When primary users are present, we characterize and analyze the connectivity for all the regions: channel abundance, optimal, and channel deprivation. For each region we show the requirement and the outcome of using either type of rendezvous techniques. Moreover, we find the tradeoff between deployment-density versus rendezvous probability which results in a connected network. Our results can be used to decide on the goodness of any channel rendezvous algorithm by computing the expected resultant connectivity. They also provide a guideline for achieving connectivity using minimal resources.

Increasing Wireless Adhoc Network Capacity through Simultaneous Transmissions

A great deal of research has been carried out regarding increasing the capacity of wireless networks. The general findings are that increasing the number of nodes in a wireless network decreases individual throughput, simultaneous transmissions cause interference and therefore hinder capacity, and that topology control can increase network power efficiency and reduce the interference within the network. This paper demonstrates that appropriately spaced simultaneous transmissions are beneficial to the capacity of shared spectrum wireless networks and that adding nodes to a wireless network can, in fact, increase its capacity if the nodes are intelligently placed and node transmission powers are appropriately set. In this paper we firstly discuss the inefficiency of high power transmission for networks which allow simultaneous transmissions. It is then demonstrated that if multiple transmitters are utilised simultaneously with uniform transmission power, the network capacity is a local maximum if the required spacing conditions between the receivers are met. In the presence of background noise one can determine that this configuration represents the maximum network capacity achievable. The required separation is defined for the general case and shown to decrease as the number of simultaneous transmissions increases. This result is verified through simulations which demonstrate the construction of high capacity networks. Simulations are also presented which show how existing networks can be augmented with additional nodes and a reduction of transmission power, to exhibit higher uniform average network capacities.

Multihop cellular: from research to systems, standards, and applications [Guest Editorial

It has been more than a decade since the multihop cellular network (MCN) architecture was first proposed and analyzed in 2000 [1]. As the transmission range decreases <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> times, the number of simultaneous transmissions and hop count increase by <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> times and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> times, respectively, which leads to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i> times cellular capacity increase. Fundamental research projects have demonstrated the benefits of MCN in terms of system capacity, service coverage, and network connectivity. Many special issues have been devoted to this stream of research [2–6]. The actual concept behind the MCN architecture could be regarded as a hybrid of mobile ad hoc networks (MANETs) and cellular networks. This concept of "relaying within a cell" also pushed standard bodies to consider solutions embedded with mesh or ad hoc architectures, such as IEEE 802.11s [7], IEEE 802.15.5 [8], and IEEE 802.16j [9]. Now, in the recent standards of the Third Generation Partnership Project (3GPP), Proximity-Based Services (ProSe) [10, 11] related work items also cover the MCN concept. In addition to device-to-device (D2D) direct communications, user equipment (UE)–UE relay and UE–network relay are also supported features. Both infrastructural and infrastructureless architectures are considered. Among many use cases, the most urgent one is public safety. These show that MCN architecture realization is ongoing.

An optical CDMA system based on chaotic sequences

In this paper, a coherent asynchronous optical code division multiple access (OCDMA) system is proposed, whose encoder/decoder is an all-optical generator. This all-optical generator can generate analog and bipolar chaotic sequences satisfying the logistic maps. The formula of bit error rate (BER) is derived, and the relationship of BER and the number of simultaneous transmissions is analyzed. Due to the good property of correlation, this coherent OCDMA system based on these bipolar chaotic sequences can support a large number of simultaneous users, which shows that these chaotic sequences are suitable for asynchronous OCDMA system.

Framework for Analysis of Transmission Rate Scheduling for Wireless CDMA Data Networks

The optimal utilization of network resources and the capacity to fulfill quality of service requirements are key requirements for 3rd G networks operations. Several burst admission and transmission rate scheduling algorithms are proposed in the literature. In this study, we develop an analytical framework for the downlink transmission rate scheduling problem for CDMA networks employing discrete service bit rates. The framework uses the average downlink transmit power as the system state and develops a K-dimensional Markov chain representing all possible states in the system. In addition, the transition probabilities due to arrivals of burst requests are made a function of the power utilization and the average power required to support the new burst taking into account the path loss model. The study assumes a transmission rate assignment scheme where the maximum possible system bit rate is assigned given the current system state and the subscriber's eligibility profile for particular system service rates. The analytical model provides performance metrics such as system throughput, average power utilization, average number of simultaneous transmissions, burst request blocking probability, and mean burst service time. While the developed model is applicable for a general CDMA based network with arbitrary discrete system service bit rates, the model is evaluated for the example of a cdma2000 1xRTT network. A comparison between simulation and analytic results to assess the accuracy of the model is provided.

A comparison of reverse link access schemes for next-generation cellular systems

We consider different transmission options on the reverse link of cellular systems for packet data. The different transmission options are classified based on the nature of in-cell and out-of-cell interference power statistics. The categories are: (a) no in-cell interference, averaged out-of cell interference; (b) no in-cell interference, bursty out-of-cell interference; and (c) averaged in-cell interference, averaged out-of-cell interference. Depending on whether the reverse link transmission is time multiplexed one user at a time transmission, or simultaneous transmission by multiple users with or without in-cell orthogonality, the interference structure falls into one of the above three categories. We analyze the throughput performance of the system in each of these cases when incremental redundancy is employed to combat uncertainty in the interference power. We compare the different options under an in-cell rise-over-thermal (IROT) constraint and provide some insights for reverse link design for next-generation cellular systems. Our results show that transmission option (a) with an optimal choice of the number of simultaneous transmissions within the cell has the best performance over several different scenarios. Time-multiplexed transmissions, despite the bursty out-of-cell interference power structure, has throughput comparable to that of a multiple-user orthogonal transmission system for small cells where mobiles have sufficient transmit power to meet the target IROT.

Multiple-capture performance of DS-SS packet radio systems with common spreading code

The author presents a multiple-capture model for the centralised spread-spectrum (SS) packet radio systems in which each user is assigned common direct-sequence (DS) spreading code for packet transmission. Basic equations for the multiple-capture probability and throughput performance are derived at the central receiver. At the link-level, two key design parameters in common spreading code systems are evaluated, namely, the expected number of packets captured at the receiver and the allowable number of simultaneous transmissions that are supportable at a specified data bit-error rate and probability of packet capture. Using the block oriented systems simulator (BOSS), simulations were carried out for the central receivers with coherent, differential, and envelope header detection, and results from the simulations are compared with theoretical evaluations of the multiple-capture probability. It is shown, for a threshold approximation to the probability of data packet success, that the multiple-capture model significantly improves system throughput.

Direct-Sequence Spread-Spectrum Multiple-Access Communications Over Nonselective and Frequency-Selective Rician Fading Channels

An accurate approximation is obtained for the average probability of error in an asynchronous binary direct-sequence spreadspectrum multiple-access communications system operating over nonselective and frequency-selective Rician fading channels. The approximation is based on the integration of the characteristic function of the multiple-access interference which now consists of specular and scatter components. For nonselective fading, the amount of computation required to evaluate this approximation grows linearly with the product KN , where K is the number of simultaneous transmitters and N is the number of chips per bit. For frequency-selective fading, the computational effort grows linearly with the product KN2. The resulting probability of error is also compared with an approximation based on the signal-to-noise ratio. Numerical results are presented for specific chip waveforms and signature sequences.